Granulomas are localized inflammatory lesions critical to the pathology of some autoimmune diseases and to the containment of a variety of infectious agents. Granulomatous immune responses are a form of delayed-type hypersensitivity, and CD4 T cells are crucial in the initiation, regulation and resolution of these lesions. Granulomas control and prevent dissemination of mycobacteria, but they also provide a long-term host reservoir for the bacteria. The interaction between the immune system and mycobacteria within these lesions is an important aspect of mycobacterial diseases. Gaining a better understanding of how T cells regulate granulomas could potentially provide critical information for the cure of granulomatous diseases and for the development of improved vaccines. Under the aegis of our previous funding period, we have developed new granuloma models and technologies to study them. We described different roles of pathogen-specific and non-specific T cells in granuloma f ormation and maintenance. This continuation proposal builds on this strong foundation of basic information to address the complex questions of how T cells with different specificities and functionalities interact within granulomas. ? In the first specific aim we propose to study how CD4 T cells interact in granulomas to influence and provide a protective function. We will infect TCR transgenic RAG-/- mice that have been adoptively transferred with other TCR transgenic T cells with recombinant BCG that express fusion proteins expressing one, two, or three of the corresponding T cell epitopes. We will examine T cell function, granuloma formation, and protection against mycobacterial growth to determine how T cells specific for the pathogen interact and how that interaction may influence the granuloma phenotype and anti-mycobacterial function. These studies will allow us to compare systemic and local immunodominance and the mechanism(s) by which multi-epitope vaccines may work. I n the second and third specific aims we will investigate whether anergic and/or regulatory T cells home to granulomas and how these cells regulate the granulomatous reaction during both acute and chronic stages of infection. This new knowledge may lead to therapies by which granulomatous diseases can be treated by modifying T cell responses.These studies address immunoregulatory mechanisms by T cells to control acute and chronic granulomas in a model of BCG infection. Granuloma is the hallmark of many infectious and autoimmune diseases. They contribute to protection against infectious pathogens and to infection- or autoimmunity-induced pathology. New knowledge of how T cells regulate granulomas will lead to more efficient therapeutic manipulations of granulomatous diseases.